阅读说明：本技术 印刷配线板及其制造方法 (Printed wiring board and method for manufacturing same ) 是由 冈本康平 三浦宏介 上田宏 酒井将一郎 池边茉纪 于 2017-12-22 设计创作，主要内容包括：根据本发明的一方面的印刷配线板包括具有绝缘特性的基膜和层叠在基膜的至少一个表面上包含排列设置的多个配线部分的导电图案。每个配线部分具有第一导电部分和涂覆在第一导电部分的外表面上的第二导电部分。每个配线部分的平均宽度为10μm以上至50μm以下。第二导电部分的平均厚度为1μm以上至小于8.5μm。根据本发明不同方面的印刷配线板制造方法包括通过在抗蚀剂图案的开口镀覆导电基础层形成构成配线部分的第一导电部分的第一导电部分形成步骤；去除抗蚀剂图案及其底部的导电基础层的导电基础层去除步骤；以及通过镀覆用第二导电部分覆盖第一导电部分的外表面的第二导电部分覆盖步骤。(A printed wiring board according to an aspect of the present invention includes a base film having an insulating property and a conductive pattern including a plurality of wiring portions arranged in an array, laminated on at least one surface of the base film. Each of the wiring portions has a first conductive portion and a second conductive portion coated on an outer surface of the first conductive portion. The average width of each wiring portion is 10 [ mu ] m or more and 50 [ mu ] m or less. The second conductive portion has an average thickness of 1 μm or more and less than 8.5 μm. A printed wiring board manufacturing method according to various aspects of the present invention includes a first conductive portion forming step of forming a first conductive portion constituting a wiring portion by plating a conductive base layer on an opening of a resist pattern; a conductive base layer removing step of removing the resist pattern and the conductive base layer at the bottom thereof; and a second conductive portion covering step of covering an outer surface of the first conductive portion with a second conductive portion by plating.)

1. A printed wiring board comprising:

a base film having an insulating property; and

a conductive pattern including a plurality of wiring portions laminated to extend on at least one surface of the base film,

wherein each wiring portion includes a first conductive portion and a second conductive portion coated on an outer surface of the first conductive portion,

an average width of each wiring portion is 10 μm or more and 50 μm or less, and an average thickness of the second conductive portion is 1 μm or more and less than 8.5 μm.

2. The printed wiring board according to claim 1,

wherein the average interval of each wiring portion is 3 μm or more and 20 μm or less.

3. The printed wiring board according to claim 1 or 2,

wherein a ratio of an average width of an upper surface of the first conductive portion to an average width of a bottom surface of the first conductive portion is 0.5 or more and 1.0 or less, and

the ratio of the average width of the upper surface of each wiring portion to the average width of the bottom surface of each wiring portion is 0.7 or more and 1.5 or less.

4. The printed wiring board according to any one of claims 1, 2, and 3,

wherein a ratio of an average height of each wiring portion to an average height of the first conductive portion is 1.05 or more and 5 or less.

5. A method for manufacturing a printed wiring board, the printed wiring board comprising: a base film having an insulating property; and a conductive pattern including a plurality of wiring portions laminated to extend on at least one surface of the base film, the method including:

a conductive base layer laminating step of laminating a conductive base layer on the one surface of the base film;

a photoresist film laminating step of laminating a photoresist film on one surface of the conductive base layer;

a resist pattern forming step of forming a resist pattern having an inverted shape of the conductive pattern by exposure and development of the photoresist film;

a first conductive portion forming step of forming a first conductive portion for forming each wiring portion by plating an opening of the resist pattern on the conductive base layer;

a conductive base layer removing step of removing the resist pattern and the conductive base layer at the bottom of the resist pattern; and

a second conductive portion coating step of coating a second conductive portion on an outer surface of the first conductive portion by plating,

wherein an average width of each wiring portion is 10 μm or more and 50 μm or less, and an average thickness of the second conductive portion is 1 μm or more and less than 8.5 μm.

6. The method for manufacturing a printed wiring board according to claim 5,

wherein in the conductive base layer removing step, the conductive base layer is removed by etching, and an average etching amount of the first conductive portion is 0.3 μm or more and less than 3.5 μm.

Technical Field

The present invention relates to a printed wiring board and a method for manufacturing the printed wiring board. The present application claims priority from japanese application No.2017-97663 filed on 5, 16/2017 and contains all the contents described in the above japanese application.

Background

Printed wiring boards are widely used along with the miniaturization of electronic devices. A method for forming a wiring pattern of a printed wiring board is, for example, a semi-additive method. In the semi-additive method, an underlying metal layer is formed on a base film mainly made of polyimide, a resist layer is laminated on the front surface of the underlying metal layer, and exposure and development are provided to form a resist pattern. Then, plating is provided on the base metal layer exposed in the groove of the resist pattern to form a wiring pattern having an inverted shape of the resist pattern. After that, the resist pattern is stripped, and the base metal layer is etched using the wiring pattern as ｃA mask (see japanese laid-open patent publication No. jp- ｃA-2011-.

In recent years, the wiring density of printed wiring boards has increased due to further miniaturization of electronic devices. In a printed wiring board having a high wiring density, since the wiring width is extremely small, a process step of securing the cross-sectional area of the wiring is generally performed by providing secondary plating on the wiring pattern that is scraped off by etching the above-described base metal layer.

Patent document

Patent document 1: japanese laid-open patent publication No.2011-

Disclosure of Invention

A printed wiring board according to an aspect of the present invention includes: a base film having an insulating property; and a conductive pattern including a plurality of wiring portions laminated to extend on at least one surface of the base film, wherein the wiring portions include a first conductive portion and a second conductive portion coated on an outer surface of the first conductive portion, wherein an average width of the wiring portions is 10 μm or more and 50 μm or less, and an average thickness of the second conductive portion is 1 μm or more and less than 8.5 μm.

A method for manufacturing a printed wiring board according to an aspect of the present invention is a method for manufacturing a printed wiring board, the printed wiring board including: a base film having an insulating property; and a conductive pattern including a plurality of wiring portions laminated to extend on at least one surface of the base film, the method including: a conductive base layer laminating step of laminating a conductive base layer on one surface of a base film; a photoresist film laminating step of laminating a photoresist film on one surface of the conductive base layer; a resist pattern forming step of forming a resist pattern having an inverted shape of the conductive pattern by exposure and development of the photoresist film; a first conductive portion forming step of forming a first conductive portion by plating an opening of a resist pattern on the conductive base layer, the first conductive portion forming a wiring portion; a conductive base layer removing step of removing the resist pattern and the conductive base layer at the bottom of the resist pattern; and a second conductive portion coating step of coating a second conductive portion on an outer surface of the first conductive portion by plating, wherein an average width of the wiring portion is 10 μm or more and 50 μm or less, and an average thickness of the second conductive portion is 1 μm or more and less than 8.5 μm.

Drawings

Fig. 1 is a sectional view schematically showing a printed wiring board according to an aspect of the present invention.

Fig. 2 is a flowchart illustrating a method for manufacturing a printed wiring board according to an aspect of the present invention.

Fig. 3A is a sectional view schematically showing one step of a method for manufacturing a printed wiring board according to an aspect of the present invention.

Fig. 3B is a sectional view schematically showing another step of the method for manufacturing a printed wiring board according to an aspect of the present invention.

Fig. 3C is a sectional view schematically showing another step of the method for manufacturing a printed wiring board according to an aspect of the present invention.

Fig. 3D is a sectional view schematically showing another step of the method for manufacturing a printed wiring board according to an aspect of the present invention.

Fig. 3E is a sectional view schematically showing another step of the method for manufacturing a printed wiring board according to an aspect of the present invention.

Detailed Description

[ problem to be solved by the present disclosure ]

Heretofore, a high-density printed wiring board required a certain time for the above-mentioned secondary plating step, which is one of the reasons for increasing the variation in the size of the wiring after secondary plating and increasing the production cost of the printed wiring board. Therefore, it is desirable to shorten the secondary plating step.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a printed wiring board and a method for manufacturing a printed wiring board, in which: the manufacturing cost can be reduced while reducing the dimensional change of the wiring by shortening the secondary plating step.

[ Effect of the present disclosure ]

The printed wiring board and the method for manufacturing a printed wiring board according to an aspect of the present invention can reduce manufacturing costs while reducing variations in wiring size by shortening the secondary plating step.

[ description of embodiments of the invention ]

A printed wiring board according to an aspect of the present invention includes: a base film having an insulating property; and a conductive pattern including a plurality of wiring portions laminated to extend on at least one surface of the base film, wherein each wiring portion includes a first conductive portion and a second conductive portion coated on an outer surface of the first conductive portion, an average width of the wiring portion is 10 μm or more and 50 μm or less, and an average thickness of the second conductive portion is 1 μm or more and less than 8.5 μm.

The printed wiring board includes a wiring portion including a first conductive portion formed using a semi-additive method and a second conductive portion formed using secondary plating on the first conductive portion, and an average thickness of the second conductive portion is within the above range. In other words, in the printed wiring board, the volume of the second conductive part is small relative to the first conductive part, and the time required for the secondary plating step can be shortened. Therefore, variations in the size of the wiring can be reduced, and the manufacturing cost can be reduced. Since the aspect ratio of the first conductive part can be relatively small in the printed wiring board, the first conductive part can be prevented from peeling off during the manufacturing process.

Preferably, the average interval of the plurality of wiring portions is 3 μm or more and 20 μm or less. By setting the average interval of the plurality of wiring portions within the above range, the time of the secondary plating step can be shortened while increasing the wiring density.

Preferably, a ratio of an average width of the upper surface of the first conductive portion to an average width of the bottom surface is 0.5 or more and 1.0 or less. Preferably, a ratio of an average width of the upper surface of the wiring portion to an average width of the bottom surface is 0.7 or more and 1.5 or less. In this way, when the ratio of the average width of the upper surfaces of the first conductive portion and the wiring portion with respect to the average width of the bottom surface is set to the above range, it is possible to promote shortening of the time of the secondary plating step.

Preferably, a ratio of an average height of the wiring portion to an average height of the first conductive portion is 1.05 or more and 5 or less. As above, when the ratio of the average height of the wiring portion with respect to the average height of the first conductive portion is within the above range, uniformity of the wiring size can be promoted.

A method for manufacturing a printed wiring board according to an aspect of the present invention is a method for manufacturing a printed wiring board, the printed wiring board including: a base film having an insulating property; and a conductive pattern including a plurality of wiring portions laminated to extend on at least one surface of the base film, the method including: a conductive base layer laminating step of laminating a conductive base layer on one surface of a base film; a photoresist (photoresist) film laminating step of laminating a photoresist film on one surface of the conductive base layer; a resist pattern forming step of forming a resist pattern having an inverted shape of the conductive pattern by exposure and development of the photoresist film; a first conductive portion forming step of forming a first conductive portion by plating an opening of a resist pattern on the conductive base layer, the first conductive portion forming a wiring portion; a conductive base layer removing step of removing the resist pattern and the conductive base layer at the bottom of the resist pattern; and a second conductive portion coating step of coating a second conductive portion on an outer surface of the first conductive portion by plating, wherein an average width of the wiring portion is 10 μm or more and 50 μm or less, and an average thickness of the second conductive portion is 1 μm or more and less than 8.5 μm.

In this method for manufacturing a printed wiring board, the average thickness of the second conductive parts made by secondary plating on the first conductive part formed by semi-additive method is within the above range. In other words, in this method for manufacturing a printed wiring board, since the wiring portion is formed with the volume of the second conductive portion reduced compared to the first conductive portion, the time required for the secondary plating step (second conductive portion plating step) is shortened. As a result, variations in the size of the wiring are suppressed, and the cost of manufacturing the printed wiring board can be reduced. Further, in this method for manufacturing a printed wiring board, since the aspect ratio of the first conductive part can be relatively small, the first conductive part can be prevented from peeling off during the manufacturing process.

In the above-described conductive base layer removing step, the conductive base layer may be removed by etching, and the average etching amount of the above-described first conductive portion may be 0.3 μm or more to less than 3.5 μm. By etching the first conductive portion with the average etching amount within the above range, the conductive base layer can be removed while saving the etching amount of the first conductive portion. Therefore, reduction in time for the secondary plating step can be promoted.

[ detailed description of embodiments of the invention ]

Hereinafter, a printed wiring board and a method for manufacturing a printed wiring board according to an embodiment of the present invention will be described in detail with reference to the drawings. In the printed wiring board of this embodiment, "front-back" indicates the thickness direction of the printed wiring board. The thickness direction toward the side on which the conductive patterns are stacked is referred to as "front", and the thickness direction toward the side opposite to the side on which the conductive patterns are stacked is referred to as "rear".

[ printed Wiring Board ]

The printed wiring board shown in fig. 1 mainly includes a base film 1 having insulating properties, a conductive pattern 2 laminated on one side (front surface side) of the base film 1, and an insulating layer 3 coated on outer surfaces of the base film 1 and the conductive pattern 2.

< basic film >

The base film 1 is a layer made of a synthetic resin having an electrical insulation property. Further, the base film 1 is provided to form a base for forming the conductive pattern 2. The base film 1 may be flexible, in which case the printed wiring board functions as a flexible printed wiring board.

The material of the base film 1 is not particularly limited as long as the material has insulating properties. A synthetic resin film having a low dielectric constant and formed in a sheet shape may be used. The synthetic resin film contains, for example, polyimide, polyethylene terephthalate, a liquid crystal polymer, a fluoropolymer, and the like as a main component. The term "major constituent" refers to the constituent having the highest content, for example, more than 50% by weight of the material.

The lower limit of the average thickness of the base film 1 is preferably 5 μm, and more preferably 10 μm. The upper limit of the average thickness of the base film 1 is preferably 50 μm, and more preferably 40 μm. If the average thickness of base film 1 is less than the above lower limit, the dielectric strength of base film 1 may be insufficient. On the other hand, if the average thickness of the base film 1 exceeds the above upper limit, the printed wiring board may become unnecessary.

< conductive Pattern >

The conductive pattern 2 is a layer made of a conductive material and includes a plurality of wiring portions 2a arranged in an extended manner. The wiring portion 2a is, for example, wiring forming a coil pattern. The conductive pattern 2 may include a pattern such as a pad portion or the like in addition to the wiring portion 2 a. The conductive pattern 2 may be directly laminated onto the surface of the base film 1 or laminated onto the surface of the base film 1 via an adhesive layer.

The material (main component) of the conductive pattern 2 is not particularly limited as long as the material has conductivity. However, it is preferred that the material has a low electrical resistance. The conductive pattern 2 may be made of, for example, copper, silver, or the like. The conductive pattern 2 may be plated with gold, silver, tin, nickel, or the like.

Each of the plurality of wiring portions 2a includes a first conductive portion 2b and a second conductive portion 2c coated on an outer surface of the first conductive portion 2 b. Specifically, the first conductive part 2b is laminated on the front surface side of the base film 1, has a line pattern in a plan view, and forms a frame of the wiring part 2 a. The second conductive part 2c is coated on the outer surface of the first conductive part 2b except the surface facing the base film 1 (directly laminated on the base film 1 or laminated on the base film 1 via another layer), as shown in fig. 1. In other words, the first conductive portion 2b is covered with the base film 1 and the second conductive portion 2 c.

The first conductive part 2b and the second conductive part 2c are each made of a plating layer formed by plating. The first conductive part 2b and the second conductive part 2c may be formed of the same kind of material, or may be formed of different materials. In addition, the first conductive portion 2b includes a conductive base layer used in the semi-additive method and a plating layer formed on the conductive base layer.

The lower limit of the average width w0 of the plurality of wiring portions 2a is 10 μm, preferably 15 μm, and more preferably 20 μm. On the other hand, the upper limit of the average width w0 of the plurality of wiring portions 2a is 50 μm, preferably 45 μm, and more preferably 40 μm. If the average width w0 of the plurality of wiring portions 2a is less than the above-described lower limit, manufacturing may become difficult. In contrast, if the average width w0 of the plurality of wiring portions 2a exceeds the above upper limit, the wiring density may not satisfy the requirement. The "average width of the plurality of wiring portions" is a value obtained by averaging the maximum width of the wiring portions in a cross section perpendicular to the longitudinal direction of the wiring portions along the longitudinal direction of the wiring portions, and the same applies to the first conductive portion described below. As used herein, the "average value" is an average value of values measured at a plurality of points in the measurement object.

As the lower limit of the ratio of the average width of the upper surface to the average width of the bottom surface of the wiring portion 2a, 0.7 is preferable, 0.85 is more preferable, and 0.90 is further preferable. On the other hand, as the upper limit of the ratio, 1.5 is preferable, 1.4 is preferable, and 1.3 is further preferable. If the above ratio is less than the above lower limit, the cross-sectional area of the wiring portion 2a may be small and the resistance may be excessively large. In contrast, if the above ratio exceeds the above upper limit, the wiring portions 2a may be easily peeled off, and the adjacent wiring portions 2a may contact each other, causing a short circuit. The "average width of the bottom surface of the wiring portion" is a value obtained by averaging the width of the base film side of the wiring portion in a cross section perpendicular to the longitudinal direction of the wiring portion in the longitudinal direction of the wiring portion, and the "average width of the upper surface of the wiring portion" is a value obtained by averaging the widths of the wiring portion in the above-described cross section on the opposite side of the base film in the longitudinal direction of the wiring portion, and the same applies to the first conductive portion described later.

The lower limit of the average interval d of the plurality of wiring portions 2a is preferably 3 μm, more preferably 5 μm, and further preferably 7 μm. Meanwhile, the upper limit of the wiring portion 2a is preferably 20 μm, more preferably 17 μm, and further preferably 15 μm. If the average interval d of the plurality of wiring portions 2a is smaller than the above-described lower limit, short circuits may occur between the wiring portions 2 a. In contrast, if the average interval d of the plurality of wiring portions 2a exceeds the above upper limit, the wiring density may not satisfy the requirement. The "average interval of the plurality of wiring portions" is a value obtained by averaging the minimum distances between the opposite sides of the adjacent wiring portions in a cross section perpendicular to the longitudinal direction of the wiring portions along the longitudinal direction of the wiring portions.

As the lower limit of the average height h0 of the plurality of wiring portions 2a, 20 μm is preferable, 30 μm is preferable, and 40 μm is further preferable. On the other hand, as the upper limit of the average height h0 of the plurality of wiring portions 2a, 100 μm is preferable, 70 μm is preferable, and 50 μm is further preferable. If the average height h0 of the plurality of wiring portions 2a is less than the above-described lower limit, the resistance of the wiring portions 2a may become excessively large as the wiring density increases. In contrast, if the average height h0 of the plurality of wiring portions 2a exceeds the above upper limit, the printed wiring board may become unnecessarily thick. The "average height of the plurality of wiring portions" is a value obtained by averaging the maximum height of the wiring portions in a cross section perpendicular to the longitudinal direction of the wiring portions along the longitudinal direction of the wiring portions, and the same applies to the first conductive portion described below.

As the lower limit of the average aspect ratio of the plurality of wiring portions 2a, 1.2 is preferable, 1.4 is preferable, and 1.6 is further preferable. On the other hand, as the upper limit of the average aspect ratio of the plurality of wiring portions 2a, 3.0 is preferable, 2.5 is preferable, and 2.0 is further preferable. If the average aspect ratio of the plurality of wiring portions 2a is less than the above-described lower limit, the wiring density may not satisfy the requirement. In contrast, if the average aspect ratio of the plurality of wiring portions 2a exceeds the above upper limit, it may be difficult to manufacture. The "aspect ratio of the plurality of wiring portions" is a ratio of the above average height to the above average width, and the same applies to the first conductive portion described later.

In the wiring portion 2a forming the coil pattern, it is preferable that the cross-sectional area (average width, average height, and average aspect ratio) of each of the plurality of wiring portions 2a is equal.

The lower limit of the average width w1 of the first conductive portions 2b of the plurality of wiring portions 2a is preferably 1 μm, more preferably 5 μm, and further preferably 10 μm. Meanwhile, the upper limit of the average width w1 of the first conductive portion 2b is preferably 40 μm, more preferably 30 μm, and further preferably 20 μm. If the average width w1 of the first conductive part 2b is less than the above lower limit, it may be difficult to form a resist pattern, or it may be difficult to peel the first conductive part 2b from the base film 1. In contrast, if the average width w1 of the first conductive portion 2b exceeds the above upper limit, the wiring density may not meet the requirement, or the resist may become difficult to peel.

The lower limit of the ratio of the average width of the upper surface of the first conductive portion 2b to the average width of the bottom surface is preferably 0.5, more preferably 0.65, and further preferably 0.7. On the other hand, the upper limit of the above ratio is preferably 1.0, and more preferably 0.9. If the above ratio is less than the above lower limit, the thickness of the second conductive portion 2c may easily vary, which may result in difficulty in manufacturing the wiring portion 2 a. In contrast, if the above ratio exceeds the above upper limit, it may be difficult to coat the outer surface of the first conductive part 2b with the second conductive part 2 c.

The lower limit of the average height h1 of the first conductive portions 2b of the plurality of wiring portions 2a is preferably 15 μm, more preferably 25 μm, and further preferably 35 μm. Meanwhile, the upper limit of the average height h1 of the first conductive part 2b is preferably 95 μm, more preferably 65 μm, and further preferably 45 μm. If the average height h1 of the first conductive portion 2b is less than the above-described lower limit, the resulting height of the wiring portion 2a becomes small, possibly causing the wiring portion 2a to become excessively large in resistance as the wiring density increases. In contrast, if the average height h1 of the first conductive part 2b exceeds the above upper limit, the printed wiring board may become unnecessarily thick.

The lower limit of the ratio (h0/h1) of the average height h0 of the wiring portion 2a to the average height h1 of the first conductive portion 2b is preferably 1.05, and more preferably 1.2. On the other hand, the upper limit of the ratio is preferably 5, and more preferably 4. If the above ratio is less than the above lower limit, the height of the resulting wiring portion 2a cannot be sufficiently increased, and the resistance of the wiring portion 2a may be excessively large. In contrast, if the above ratio exceeds the above upper limit, the height of the wiring portion 2a may easily vary in the longitudinal direction, making it difficult to manufacture the wiring portion 2 a.

The lower limit of the average aspect ratio of the first conductive portions 2b of the plurality of wiring portions 2a is preferably 2.0, more preferably 2.5, and further preferably 3.0. On the other hand, the upper limit of the average aspect ratio of the first conductive portion 2b is preferably 6.0, more preferably 5.0, and further preferably 4.0. If the average aspect ratio of the first conductive portion 2b is less than the above lower limit, the wiring density may not satisfy the requirement. In contrast, if the average aspect ratio of the first conductive portions 2b exceeds the above upper limit, it may be difficult to form a resist pattern, or the first conductive portions 2b may be easily peeled off from the base film 1.

The lower limit of the average thickness of the second conductive portion 2c is preferably 1 μm, more preferably 5 μm, and further preferably 6 μm, and 7 μm is more preferable. On the other hand, the average thickness of the second conductive portion 2c is less than 8.5 μm, preferably at most 8.0 μm, and more preferably at most 7.8 μm. If the average thickness of the second conductive portion 2c is less than the above-described lower limit, the height and width of the resulting wiring portion 2a may be reduced, and thus the resistance of the wiring portion 2a may be excessively large. On the other hand, by reducing the average thickness of the second conductive portion 2c to less than the above upper limit, the time for the secondary plating can be shortened, thereby reducing the variation in size and reducing the manufacturing cost. The "average thickness of the second conductive portion" is a value obtained by dividing the area of the second conductive portion in a cross section perpendicular to the longitudinal direction of the wiring portion by the length of the contact surface (interface) between the first conductive portion and the second conductive portion as a thickness and averaging the thickness along the longitudinal direction of the wiring portion. The length of the contact surface can be obtained by image analysis of a micrograph.

< insulating layer >

The insulating layer 3 is a layer that mainly protects the conductive pattern 2 in the printed wiring board, and a commercially available solder resist and a cover lay are used. The material of the insulating layer 3 is not particularly limited as long as it has insulating properties. As the main component of the material, resins such as polyimide, epoxy resin, phenol resin, acrylic resin, polyester, thermoplastic polyimide, polyethylene terephthalate, fluorinated resin, liquid crystal polymer, and the like can be used.

The lower limit of the average thickness of the insulating layer 3 (average distance from the surface of the base film 1 to the outer surface of the insulating layer 3) is preferably 25 μm, more preferably 35 μm, and further preferably 45 μm. On the other hand, the upper limit of the average thickness of the insulating layer 3 is preferably 200 μm, more preferably 180 μm, and further preferably 160 μm. If the average thickness of the insulating layer 3 is less than the above lower limit, the insulation may become insufficient. In contrast, if the average thickness of the insulating layer 3 exceeds the above upper limit, the printed wiring board may become unnecessarily thick.

[ method for manufacturing printed Wiring Board ]

As shown in fig. 2, the method for manufacturing a printed wiring board mainly includes: a conductive base layer laminating step S1 for laminating a conductive base layer on one surface of the base film; a photoresist film laminating step S2 for laminating a photoresist film on one surface of the conductive base layer; a resist pattern forming step S3 for forming a resist pattern having an inverted shape of the conductive pattern by exposure and development of the photoresist film; a first conductive portion forming step S4 for forming a wiring portion of the conductive pattern by plating an opening of the resist pattern on the conductive base layer; a conductive base layer removing step S5 for removing the resist pattern and the conductive base layer at the bottom of the resist pattern; and a second conductive part coating step S6 for coating the second conductive part on the outer surface of the first conductive part by plating.

< conductive base layer Forming step >

In the conductive base layer forming step S1, as shown in fig. 3A, a conductive base layer S is formed on the front surface of the base film 1 by, for example, applying and firing a metal particle dispersion liquid by electroless plating.

(conductive base layer)

The conductive base layer S serves as an object (cathode) of the plating in the first conductive portion forming step S4 (to be described later).

The lower limit of the average thickness of the conductive base layer S is preferably 50nm, and more preferably 100 nm. On the other hand, the upper limit of the average thickness of the conductive base layer S is preferably 2 μm, and more preferably 1.5 μm. If the average thickness of the conductive base layer S is less than the above lower limit, the first conductive portion 2b may not be formed to have a uniform thickness because the continuity of the conductive base layer S cannot be ensured. In contrast, if the average thickness of the conductive base layer S exceeds the above upper limit, the cost of manufacturing the printed wiring board may be unnecessarily increased.

When the conductive base layer S is formed by electroless plating, for example, nickel, copper, cobalt, gold, silver, tin, or the like, or an alloy thereof may be used as a material of the conductive base layer S. Among them, nickel, copper and cobalt, which can be relatively easily increased in thickness by autocatalysis, are preferably used.

< Photoresist film laminating step >

In the photoresist film laminating step S2, a photoresist film R0 is laminated onto the surface of the conductive base layer S, as shown in fig. 3B.

The photoresist film R0 is made of a negative resist composition in which bonding of polymers is enhanced by exposure to light to decrease solubility in a developer, or a positive resist composition in which bonding of polymers is reduced by exposure to light to increase solubility in a developer.

The photoresist film R0 may be formed on the conductive base layer S by coating a liquid resist composition and drying it, but it is preferable to laminate a dry film photoresist that is not flowable at room temperature by hot-press deposition. By using a dry film photoresist as the photoresist film R0, the thickness of the photoresist film R0 can become uniform and small. Therefore, miniaturization of the resist pattern can be promoted.

The lower limit of the average thickness of the photoresist film R0 is preferably 20 μm, and more preferably 40 μm. On the other hand, the upper limit of the average thickness of the photoresist film R0 is preferably 120 μm, and more preferably 80 μm. If the average thickness of the photoresist film R0 is less than the above lower limit, the dry film resist may not be easily handled. On the other hand, if the average thickness of the photoresist film R0 exceeds the above upper limit, the accuracy of the shape of the resist pattern may be lowered.

< resist Pattern Forming Process >

In the resist pattern forming step S3, first, the photoresist film R0 is formed to have a portion dissolved in a developing solution and a portion not dissolved in the developing solution, for example, by selectively exposing the photoresist film R0 with a photomask or the like.

Subsequently, the highly soluble portion of the photoresist film R0 is washed away using a developer to obtain a resist pattern R1 in which the portion corresponding to the first conductive portion 2b to be formed is an opening, as shown in fig. 3C.

The resist pattern R1 has a plurality of openings defining the first conductive portions 2 b. The lower limit of the average width w2 of the openings is preferably 5 μm, more preferably 10 μm, and further preferably 15 μm. Meanwhile, the upper limit of the average width w2 of the opening is preferably 45 μm, more preferably 35 μm, and further preferably 25 μm. If the average width w2 of the openings is less than the above lower limit, the width of the openings may vary significantly. In addition, the thickness (secondary plating amount) of the second conductive part 2c may fall outside the above range, resulting in a variation in size and an increase in the cost of manufacturing the printed wiring board. In contrast, if the average width w2 of the openings exceeds the above upper limit, the resist pattern R1 may be easily peeled off, and the wiring density may not satisfy the requirement. The average width of the openings corresponding to the first conductive portions 2b of the resist pattern R1 is the same as the average width of the first conductive portions 2b before etching in the conductive base layer removing step S5 described later.

< first conductive portion Forming step >

In the first conductive portion forming step S4, as shown in fig. 3D, the first conductive portion 2b is formed by laminating a metal onto the conductive base layer S exposed from the opening of the resist pattern R1 by electroplating. The first conductive portion 2b includes a plating layer formed by electroplating, and a conductive base layer S.

Specifically, in the first conductive portion forming step S4, the base film 1, the conductive base layer S, the laminate of the resist pattern R1, and the electrode of the laminate facing the resist pattern R1 are arranged in an electrolyte solution, the negative electrode of a direct current power source is connected to the conductive base layer S, and the positive electrode is connected to the opposite electrode, so that the metal in the electrolyte is deposited on the surface of the conductive base layer S.

As the metal laminated by electroplating, that is, the metal forming the first conductive portion 2b, for example, copper, nickel, gold, silver, platinum, or the like can be used. Among them, copper, which is relatively inexpensive and has excellent conductivity, and nickel, which is relatively inexpensive and has excellent corrosion resistance, are preferably used.

As the lower limit of the average height of the first conductive portion 2b before etching formed in the first conductive portion forming step S4, 20 μm is preferable, 30 μm is preferable, and 38 μm is further preferable. On the other hand, the upper limit of the average height of the first conductive portion 2b before etching is preferably 100 μm, more preferably 70 μm, and further preferably 50 μm. If the average height of the first conductive parts 2b before etching is less than the above-described lower limit, the thickness (secondary plating amount) of the second conductive parts 2c may deviate from the above-described range, resulting in variations in size and an increase in the cost of manufacturing the printed wiring board. In contrast, if the average height of the first conductive parts 2b before etching exceeds the above upper limit, the resist may become difficult to peel off, or the printed wiring board may become unnecessarily thick.

< conductive base layer removal step >

In the conductive base layer removing step S5, after the first conductive part 2b is formed, the resist pattern R1 and the conductive base layer S at the bottom thereof are removed, as shown in fig. 3E.

The resist pattern R1 is removed by peeling the resist pattern R1 from the conductive base layer S. Specifically, the laminated body including the resist pattern R1, the first conductive part 2b, the conductive base layer S, and the base film 1 is immersed in a stripping liquid, thereby swelling the resist pattern R1 with the stripping liquid. This causes repulsive force between the resist pattern R1 and the conductive base layer S, and the resist pattern R1 is peeled off from the conductive base layer S. Known stripping liquids may be used.

The conductive base layer S at the bottom of the resist pattern is removed by etching the conductive base layer S exposed after the resist pattern is stripped using the first conductive portion 2b as a mask. Thus, the plurality of first conductive portions 2b are electrically separated. The etching uses an etchant that etches the metal forming the conductive base layer S.

The etching amount may be an amount by which the conductive base layer S is completely removed. However, in the method for manufacturing a printed wiring board, the average etching amount of the first conductive part 2b is preferably 0.3 μm or more to less than 3.5 μm. More preferably, the average etching amount is 2.0 μm or less. By setting the above average etching amount to the above range, the ratio of the average width of the upper surface to the average width of the bottom surface of the first conductive portion 2b can be set to 0.5 or more and 1.0 or less, and since the size of the first conductive portion 2b after etching can be increased, shortening of the time of the secondary plating step can be promoted. The "average etching amount of the first conductive portion" is an average value of the following thicknesses averaged along the longitudinal direction of the wiring portion: the thickness is a value obtained by dividing a difference between an area of the first conductive portion before etching and an area of the first conductive portion after etching in a cross section perpendicular to the wiring portion by a length of an outer surface (excluding a lamination surface having the base film) of the first conductive portion before etching.

< second conductive portion coating step >

In the second conductive portion coating step S6, the second conductive portion 2c is coated on the outer surface of the first conductive portion 2b by plating to form the wiring portion 2 a. The plating may be performed by, for example, a known electroplating method. Thus, a printed wiring board shown in FIG. 1 was obtained in which the average width of the wiring portion 2a was 10 μm or more and 50 μm or less and the average thickness of the second conductive portion 2c was 1 μm or more and less than 8.5 μm.

< advantages >

The printed wiring board includes a wiring portion 2a made of a first conductive portion 2b formed by a semi-additive method and a second conductive portion 2c formed by secondary plating on the first conductive portion 2b, and the average thickness of the second conductive portion 2c is within the above range. In other words, since the volume of the second conductive part 2c is small relative to the first conductive part 2b and the time required for the secondary plating step in the printed wiring board can be shortened, variations in the size of the wiring can be suppressed and the manufacturing cost can be reduced. Further, in the method for manufacturing a printed wiring board, the aspect ratio of the first conductive part 2b can be relatively small, so that the first conductive part 2b can be prevented from peeling off during manufacturing.

Since the wiring density of the printed wiring board is improved to be high while maintaining the dimensional accuracy of the wiring, the printed wiring board can be suitably used for an actuator, an antenna, a transformer, and the like of a small-sized device.

[ other examples ]

The embodiments disclosed herein are illustrative in all respects and should not be considered restrictive. The scope of the present invention is not limited to the structure of the above-described embodiments, but is described by the claims, and is intended to include all changes within the meaning and scope equivalent to the claims.

Although the above-described embodiment describes a printed wiring board having a single base film and a layer of conductive patterns laminated on one surface of the base film, it is within the scope of the present invention that the conductive patterns are laminated on both surfaces of the single base film. Further, the printed wiring board may be a multilayer printed wiring board that includes a plurality of base films each having a conductive pattern on one or both surfaces.

Description of the reference numerals

1 base film

2 conductive pattern

2a wiring part

2b first conductive part

2c second conductive part

3 insulating layer

R0 photoresist film

R1 resist pattern

S conductive base layer

S1 conductive base layer laminating step

S2 photoresist film laminating step

S3 resist pattern forming step

S4 first conductive portion forming step

S5 conductive base layer removing step

S6 second conductive part coating step

Average width of w0 wire section

w1 average width of first conductive part

Average width of opening part of w2

Average height of h0 wiring portion

h1 average height of first conductive part